1. Field of the Invention
The present invention relates in general to the field of information handling system circuits, and more particularly to a system and method for current measurement.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems perform most processing functions with integrated circuits (ICs), however, a number of other electrical circuits are typically included so that the ICs can communicate with each other and have power. Generally, IC communication and power circuits run through printed circuit boards (PCBs), such as a motherboard and daughter boards. The motherboard typically supports a central processing unit (CPU), chipset and memory, such as RAM, while daughter boards typically interface with the motherboard to support specific functions, like graphics. ICs typically operate with power supplied through power pins at a defined constant voltage. In some instances, the power drawn by an IC varies dramatically during normal operations, such as when a CPU transitions from an idle state having minimal computations to an active state performing complex operations. As the number of transistors on CPUs continues to increase, variations in power demanded by CPUs during normal operating conditions also tends to increase. Precise power management also presents a challenge in other information handling system applications, such as with hot-swap controllers.
Precise power management generally calls for precise current measurement at various locations throughout an information handling system. One common method of current measurement is a Hall sensor that measures the magnetic field around the current conductor. However, Hall sensors are relatively expensive. A less expensive method for current measurement is to flow the current through a precision shunt resistor and measure the voltage drop across the shunt resistor. In order to accurately measure current, the shunt resistor is built to provide a constant resistance across a variety of operating conditions, such as variations in temperature. A difficulty with shunt resistors is that the voltage drop across the shunt resistor wastes power and produces heat as a byproduct of the current measurement. Other less precise resistors are sometimes used to detect overcurrent situations. For example, a MOSFET Rdson detects an overcurrent by assuming a nominal resistance value and measuring the voltage drop across the resistance. Precise current measurements are not attempted since a precise resistance value is not known, however, for determining gross overcurrent conditions, such as might result from a short to ground, the nominal resistance value provides an accurate enough estimation.